Process of stuffing and finishing leather



Patented July 21, 1942 PROCESS OF STUFFING AND FINISHHIG LEATHER Leon B. Conant, Boston, Mass.

No Drawing.

Application February 8, 1940,

Serial No. 317,911 1 Claim. (o1. 149- 6 This invention relates to an improvement in the currying or stufilng of leather and, in particular, to its heat treatment having application throughout its preparation and character before, during and following its impregnation or permeationby heated liquids. The primary purpose of this invention is to'give beneficial effect to the saturation of the leather by a heated oleaginous liquid filler or stuffing by removing, prior to its introduction therein, all of the hygroscopic moisture in the leather by a gradually intensified and adequately applied hot dehydration and preheating thereof whereby, fOlIOWing its impregnation, the leather may be rehydrated and finished to suit. a

In my U. S. Patent No. 2,202,092 issued May 28, 1940 and entitled Process of finishing leather, I have described the rudiments or partially developed principles of my process which since have been'brought to perfection. Consequently, in this specification which supplements my previous one aforesaid, I shalldescribe the technical refinements of process as now determined and which are essential to the production of the improved leather which myprocess alone is capable of manufacturing.

.A survey of tanning and currying methods as employed throughout the leather industry establishes the fact that the use of any but a moderate degree of heat has, heretofore, always been avoided. For example, it is well known that any temperature above 200 F. comprises a heat ceiling that is universally prohibited by the tanners, since actually it is 170 F. or less that is used in currying vegetable tanned leather and 192 F. or less in stufiing chrome tanned leather; Hence, previously, to advocate the use of a temperature like 212 F. (the boiling point of water) or more has always been considered nonsense. That is to say, the tanners have all determined to their own satisfaction from experience that their employment of heat above 170 F. ruined their vegetable tanned leather and that heat above 192 F. likewise destroyed their chrome tanned leather. Since this is the reason for their common embargo of elevated temperatures, the truth appears that none of the tanners have understood how to beneficially apply elevated temperatures to leather. Now, as a matter of fact, 212 F. should be considered the mean temperature at which hygroscopic moisture is sure to be eliminated from leather. A somewhat lower temperature will do it, too, say 200 F. or a little less under controlled laboratory conditions by using a gas-heated oven, but 212 F. or more is certain because, at that body-temperature or higher, the leather, then, both has expelled its hygroscopic moisture and repels its re-entry by absorption. Such an anhydrous condition should 7 be realized to properly prepare leather for stuffing with a' hot, oleaginous filler. Moreover, the application of 212 Faupon the surface does not mean, necessarily, that equal heat has penetrated throughout the thickness of heavy leather. Hence, a higher temperature should be employed, say 215 F. Furthermore, dry steam heat should be used-never gas heat, which shrivels and impairs the quality of the leather fibres. In a laboratory trial, 200 F. may be made effective, but in a production dryer containing a thousand cubic feet or more, there is such variation of heat distribution that a safety margin as provided by super-heat should be employed in order to be sure that all of the leather has all of its hygroscopic moisture removed. In other words, the employment of say 240 F. as recorded by the temperature gauges of the dryer may, quite possibly, vary in its actual heat delivery to and heating of the leather from the ceiling of 240 F. down to a mean of say 215 F. Accordingly, the use of such elevated temperatures, as well as those even higher, is described in this specification in a manner that will clarify the problems heretofore associated with their employment.

In brief, this process is based upon the proposition that when water ceases to serve the leather fibres beneficially, then, both its further use is avoided and its presence in the leather eliminated although, be itremembered, water is indispensable, in moderation, leather. Hence, while it is true that during the working of this process, the leather is made to become absolutely anhydrous, this dehydrate condition is temporary; The final service of my process is to re-hydrate the leather. Water must be used freely during the preparation of the hide and skin for tanning, and again, as the vehicle to carry and deliver the various tanning acids and agents to and into the mass of fibres composing the thickness of the hide, whereby the fibrous structure thereof becomes tanned into leather. However, once the leather is tanned, and if desired, a modicum of oil added to prevent its oxidization, and, on occasion, colored, then, at that time, the presence in or use of water while processing it during its currying or stuifing can only result in failing to fully develop the potentialities of the leather fibres. Nevertheless heretofore, it is at this time that all vegetable tanned leather is stuffed with water-soluble fillers,

in the finished chrome tanned upper leather split, colored and fat-liquored, and, chrome sole leather stuffed with oils and greases, whereby, except in the case of one specialty sole leather, it is all performed while using water as the medium to deliver the fillers into the fibrous structure of the leather. But even so, and whatever the detail of blended filler and procedure, the heat treatment of the leather during its stuffing is, without exception, restricted to 170 F. or less for vegetable tanned leather and 192 F. or less for chrome tanned leather.

This process is an improvement in stuffing and finishing leather, any kind of leather, and, it is applicable after the tannage is completed, and, particularly while the leather is in the rough, i. e., free of stufling and uncompressed, and, containing preferably, less than 12% moisture. Both chrome and vegetable tanned sole and other heavy leather, as well as all upper leather and the like, after its splitting and coloring, should be stuffed by this process. Also, the flesh-splits thereof. Furthermore, this process is adapted to introduce all of the stufling into leather and, while it may be employed to supplement prior currying, the preference is to do the original and complete job. Moreover, While this process prohibits both the presence of water in and its application to leather during its currying or stufiing, this embargo is imposed only temporarily, since, once the leather has been stuffed or impregnated with its oleaginous filler, it is then re-hydrated in a bath of warm water and its grain surface scrubbed and cleansed, and, then, after drying but while still mellow and pliable, compression rolled and polished.

In my U. S. Patent 1,719,101, the first of several issued to me entitled Process of vulcanizing rubber to leather, I described the dehydration and preheating of leather at vulc-anizing temperatures in adaptation for its union with rubber composition during hot vulcanization. Also, in my U. S. Patent 1,769,943, I described the use of a stepped application of heat to the leather whereby its body temperature is gradually elevated from normal to an approximation of the heat of hot vulcanization in preparation for vulcanizing rubber composition thereto. The vulcanization of rubber to leather as carried out under the aforesaid patents employed a hot vulcanizing temperature ranging from 260 F. to 360 F. dependent usually upon the kind of article being made. Moreover, I recommended the use of an open heater in which to dehydrate and pre-heat the leather whose employment, when grain leather is processed, should be preceded by heating in a moderately heated and ventilated room. Flesh split leather, does not need such advance partial dehydration since it is adapted, having no grain, to be placed directly in the open heater at vulcanizing temperatures which it will absorb without injury because of its ultra porosity. Hence, in the heat preparation of leather for stufiing by a molten wax composition liquid, preferably, employed at sub-vulcanizing temperatures, i. e., never, if avoidable, above 220 F., I have benefited by employing the many lessons previously learned. Fundamental principles remain, but their application is quite different in heat-adaptation of leather for the dry heat of hot vulcanization as compared to its heat preparation for impregnation by a hot oleaginous fluid. For example, in pre-heating leathersplits for union with rubber composition during hot vulcanization, both the leather and the rubber may be assembled together and placed in a sub-vulc-anizing temperature which, then, may be gradually elevated to a scheduled vulcanizing heat comprising say a heat radius starting at 180 F. or less and ending at 260 F. or more. This practice is common in the manufacture of leather insoled, rubber outersoled canvas footwear. But, in contrast, to attempt to dehydrate and pre-heat leather without injuring it by immersion in a bath of oleaginous liquid at say F. while increasing its heat to say 200 F. could have only one result, namely, the complete ruination of the leather. Hence, it is certain that the hygroscopic moisture in the leather must have free access to a surrounding atmosphere for the dissipation of its vapors. But, however important the proper dispersion of the water-vapors from the leather may be, it is also just as essential to control their volume so that at no time shall their exit impair the quality of the fibre. Also, if the leather isto be immersed in a hot, oleaginous bath, it should be wholly anhydrous when placed therein, and, preferably, hotter than the bath. Accordingly, both my dehydrating and pre-heating of the leather are designed to secure its proper heat preparation for stuffing by this process whereby its immersion in a bath of molten wax may be accomplished successfully, preferably, at sub-vulcanizing temperatures. Hence, my processing is based on the principle of completing the heat treatment of the leather for its bath, its immersion immediately therein, and, the drying-oil of excess wax composition, all preferably, during the continued application of heat thereto. This continuous application of heat should range from say 140 F. or less to 215 F. or more as required. The leather, usually, is in the bath ten minutes or less. The bath, preferably, comprises paraffin wax blended with rubber. If desired, the wax may be cut with a suitable solvent possibly containing a small percentage of petrolatum. When the leather is immersed the bath preferably it at 200 F. and the leather at 215 F. but these temperatures are relative, only. Neither the leather nor the bath can be heated to any one pre determined temperature, and much less held there by production equipment.

After the leather has been stuffed, it cools rapidly and its wax impregnation coagulates and hardens quickly and stains the leather in semblance of mahogany. It is desirable that the leather grain surface be made to recover its natural color.- The wax stains must be removed prior to the finishing of the leather. This may be begun by dipping the leather in a wax-solvent or by washing or swabbing the grain surface with carbon tetrachloride or kerosene or other suitable hydrocarbons, and then compression rolling or kneading the residue within and below the surface. However, although this wax-solvent dressing and rolling ofthe leather grain is desirable, finishing of the leather is performed following its re-hydration. When, as the impregnated leather is soaked in a bath of heated water, preferably at a temperature above the melting point of the wax composition, say 140 F., the hot water penetrates the leather fibres and softens their wax coating and causes a film or thin skin of hydrated wax-paste to form on the surface of the grain. Whereupon, the re-hydrated leather is taken from the warm water and the excreted wax immediately removed by wiping and scrubbing. Then the wet leather should be allowed to set until its grain surface has dried out and bleached to a clean, uniform color, and then while the leather is still mellow and extra pliable it should be compression rolled to final smoothness and polished. Preferably, no caustic or other chemical agent is used in the warm water. It is understood that the grain of leather is by far its most fibrous portion, since, in it all the fibres are on end and, hence, there, their density is the greatest. Accordingly, it is on the grain that the coagulation of the wax composition is the heaviest because its surface is so closely knitted that it is hardest to penetrate, with the result that, after the impregnated leather cools to normal temperature then the wax veneer coagulated on the leather causes its entire thickness to become stiff and hard. Therefore, to make the leather after its impregnation suitably flexible, its grain should first be dressed with a wax-solvent whereby the excessive deposit of wax thereon may be removed and then given its hot water bath and final finishing. Then, the compression rolling will assure a clean, smooth and glossy surface for the grain.

When the rough surfaced impregnated leather pieces, usually either bends, bellies, shoulders or sides, are first rolled, and whether heated or not, the grain surface should be dressed with a waxsolvent whereby, as the wrinkles and irregularities in the grain are ironed out, the diluted wax is rolled in and made to penetrate into the leather. It is advisable that only the leather grain be saturated by the wax-solvent thereby allowing the hardness of the coagulated wax as deposited underneath the grain to maintain the bulk of the impregnated leather thickness. No useful purpose is served by rolling down the bulk of sole leather and reducing its thickness as is necessary when water-soluble fillers are used for stufiing it. In other words, the saturation of the wax impregnated grain of the leather by the solvent first and later by the hot water, should suffice to allow its being satisfactorily rolled without appreciably reducing its bulk. If the grain becomes well soaked with warm water and also the flesh surface, it is certain that capillary attraction will re-hydrate to completion the innermost fibres of the leather. If desired, the roller may be heated.

In putting my process to work, I take an area of leather as graded by the tanner, preferably in the rough, i. e., unstuffed and unrolled and of a thickness resulting from its tannage as passed through a wringer and dried out normally, and, then I place it in any suitable dehydrating and pre-heating dryer. are placed in the dryer together. When it is loaded, I establish therefor as uniform a temperature as is possible but, preferably, not exceeding 140 F. such approximates my initial or moderate application of heat to the leather whereby in a reasonable time the leather becomes partially dehydrated. Preferably, this level of heat is applied until the leather has been rid of at least one-third of its normal atmospheric moisture, which according to climatic conditions varies between 8% to 12% by weight. Then, I increase the heat to say 180 F. which I apply to the drying leather for another suitable period. Such approximates my medium or intermediate application of heat which further contributes to its approaching complete dehydration. It may be safely believed that now the leather has lost at least two-thirds of its original hygroscopic moisture. Then, I raise the temperature again to say 220 F. or more for another Numerous pieces of leather heat' the leather. has been made wholly anhydrous as guaranteed suitable period'during which the hot leather is" completely freed of all of its moisture, and, ac-

cordingly is now properly preheated for its hot oleaginous bath. Such approximates my elevated temperature preference for the heat preparation of the leather, but, if climatic conditions or other uncertainty makes it advisable, I again increase the heat application to say 240 F. or more. This super-heat guarantees the final adaptation of the leather but its employment should not be unduly extended. It is understood that the temperatures I have recited are relative, only, more or less heat may be applied as desired. Moreover, in place of the three 'to four steps of heat application described, two or five or more may be used. There is only one important equation, namely, that the heat be applied, from first to last, in a, manner to preserve and to' guarantee the leather all of its original fibl'OllS strength and quality. Prior to its immersion therein the body-heat of the leather should exceed that of the bath substantially, as a precautionary measure, since, actually neither any individual leather piece itself nor the wax composition bath itself is at a certain specific and uniform temperature. Allowances must be made for variables governing the mechanical and physical operation of the dryer, for irregularities of heat distribution, and, for differences of thickness and fibrous mass of the leather as well as for variations of original percentages of moisture therein. In other words, the leather, and the bath should both be heated well above the mean temperature theoretically required to eliminate all of the moisture in the leather. With say three tons of leather in the process from which approximately 600 lbs. of moisture is being extracted and then replaced by say one ton of wax, it may well be assumed that a recorded peak temperature of 232 F. may conceal small areas approaching 212 F. true heat. However, if properly performed, no more than seven hours are required to adequately dehydrate and pre- When, now, the hot leather by its preheating above 212 F. and therefore in complete preparation for its oleaginous bath, the latter should have a temperature between F. and 200 F. and the leather, a mean body-heat of not less than 215 F. to a peak of possibly 230 F. true heat. It is understood that the general temperature of the bath may be ascertained, whereas the actual body-heat energy of the hot leather, any square foot of it, is both uncertain and indeterminate. However, having finished the heat preparation of the leather, it is now immersed in the heated oleaginous bath. After a few minutes therein the impregnated leather is taken from the bath. Then, preferably while the treated leather is still warm I wet-dress the grain surface with a wax-solvent and wipe in most of the surplus wax thereon and then, after allowing the impregnated leather to cool somewhat and the wax to coagulate and harden I prefer to swab it again with the solvent and then hot enough to soften the wax whereby the excess wax deposit in the top-grain is excreted as the leather fibres absorb and their interstices receive the hot water. Actually, the hot water swollen fibres of the leather grain close together forcing much of the Water heated wax in their interstices to the surface to form a film on the grain. Now, when this film or skin-coating of hydrated waxpaste has developed so that the re-hydration of the impregnated leather is suitably underway, I remove the leather from its warm water bath and wipe the excretion of wax composition off the grain. Then, I allow the leather to complete its re-hydration and the grain surface to dry until a substantially uniform and clean color appears thereon. Then while it is still mellow and extra pliable from its hydration in the heated water, I now compression roll and polish it to requisite smoothness and lustre thereby completing its finishing. It should be understood the fibres of the grain are packed so closely and tightly together by nature that, preferably, a lesser amount of wax should be present therein in the finished material, comparatively, than in the remainder of the leather where all the wax which can advantageously be used should be deposited to impregnate the fibres thereof and their interstices. If desired, the impregnated leather may be given its hot water bath and re-hydration directly after its removal from the dryer and had its surface wet-dressed and wiped with the wax-solvent.

This process assures enduring pliability to the leather because during its re-hydration the absorption of the warm water therein, via their cores, expands the fibres and their wax coatings to suit, whereas, heretofore, when wax is introduced in solution with Water as the vehicle, its eventual drying out simply left the wax as a residue in the interstices of the leather like a silt and never as a coating impregnating its fibres. When, now the finished leather is at hand, examinaticn and testing will prove it to be impervious to cracking, porous to air, water resisting, pliably comfortable and extremely durable. Moreover, regardless f its original location in the hide, any portion of this leather whether of coarse and poor or close and prime fibrous structure, is certain to give excellent service.

In conclusion, I wish to remark that the improved quality given leather by this process is obtained by the routine of its operations, whereby the moisture is first eliminated, then, the moltenwax introduced among the dehydrated, heat absorbent fibres and then the grain washed with a wax-solvent and finally re-hydrated in warm water and finished and polished as described.

This process may be described as comprising the hot dehydration of leather in adaptation for and immersion in a bath of molten wax composition, cleaning its grain surface with a wash of wax-solvent, and then effecting its re-hydration with warm water and finally finishing it to suit. The process may be summarized as including the dehydration, impregnation and re-hydration of leather.

I claim:

The process comprising heat-dehydrating leather by applying successively relatively moderate, medium and elevated temperatures thereto progressively by dry steam heat and, while so heated, impregnating it with a hot, oleaginous liquid and then finishing it to suit.

LEON B. CONAN'I. 

